1. Field of the Invention
The present invention relates to an image forming device and image forming device control method for carrying out image forming on a sheet of paper with two-component developer by using an intermediate transfer body. In particular, the present invention relates to a technique for preventing developer from adhering to a transfer roller which presses a sheet of paper to the intermediate transfer body.
2. Description of the Related Art
There is conventionally known a technique for preventing generation of so-called “carrier attraction” in an image forming device for carrying out image forming on a sheet of paper with two-component developer including toner and carrier. In the technique, application of a predetermined potential difference to a surface of a photoreceptor by a developing device is started before processing of electrification of the surface of the photoreceptor by a charger, and the application of the predetermined potential difference to the surface of the photoreceptor by the developing device is completed after the processing of electrification of the surface of the photoreceptor by the charger is completed (a region to be electrified by the charger is positioned at an inner side of a region to which the predetermined potential difference is applied by the developing device in order to develop an electrostatic latent image to be formed in the region with the two-component developer). Accordingly, a region in which an electric field in a developing direction is created outside the region to which the processing of the electrification is applied on the surface of the photoreceptor, and a band-shaped toner image (also called a toner band) is formed intentionally.
FIG. 8 is a view showing temporal changes of the potential on the surface of the photoreceptor and the potential applied by the developing device viewed from a developing position at the time of image forming in the conventional image forming device including a mechanism for preventing generation of the carrier attraction. In FIG. 8, a shaded part is a part of the “band-shaped toner image” described above.
In the conventional image forming device, the band-shaped toner image is intentionally formed as described above. Thus, generation of a scratch on the surface of the photoreceptor due to the “carrier attraction” has been restricted to maintain image quality.
In a case of an image forming device of a so-called direct transfer system in which a toner image is formed on a surface of a photoreceptor and the toner image on the photoreceptor is directly transferred on a sheet of paper supported by an intermediate transfer body, there has not been a case where the “band-shaped toner image” formed by the conventional image forming device described above appears as a stain on an image.
However, in an image forming device with a configuration in which a toner image formed on a surface of a photoreceptor is temporarily supported by an intermediate transfer body, and then the toner image on the intermediate transfer body is transferred to a sheet of paper to be conveyed by pressing the sheet of paper to the intermediate transfer body by a transfer roller, there has been a case where toner of the “band-shaped toner image” described above adheres to a roller surface of the transfer roller. The wasteful toner adhered to the transfer roller as described above is adhered to the sheet of paper when the sheet of paper is pressed to the intermediate transfer body, and may cause deterioration in image quality.